Canine hip dysplasia remains an important problem to be solved in general veterinary practice. In less severe cases, non-operative treatment can produce satisfactory results, but more severe cases require surgical intervention.
Hip dysplasia is a painful and often debilitating condition seen most frequently in canines and is the result of an instability between the acetabulum and the femoral head. It usually results from a genetic or congenital condition wherein the acetabulum, the cup-shaped socket within the pelvis which receives the femoral head, is insufficiently formed. When the femoral head is not properly covered by the insufficient acetabulum, as the joint bears weight there is instability and the potential of injury to the surrounding tissue.
The surgical techniques for correcting hip dysplasia are known as pelvic osteotomy. This procedure provides for osteotomy of selected bone segments of the pelvis followed by rotation of the acetabular segment of the pelvis to enable better coverage of the femoral head, in order to give the canine a full range of motion for the hind legs. Typical complications, besides those associated with any surgical technique, are loss of fixation and compromise of the pelvic inlet. The loss of fixation may leave the canine patient in a worse state than before the surgery because the procedure is quite invasive requiring three pelvic osteotomies, and requires the removal of one pelvic section and the separation and rotation of another. The compromised pelvic inlet may cause chronic bowel and urinary tract problems which may only be uncomfortable, but at worse may be injurious. When coupled with the neuroses that frequently accompany such invasive surgical techniques, these complications generally render this procedure seriously flawed.
Another surgical technique has more recently been developed which requires three planar cuts in the pelvis one through the pubic ramus, one through the tuber ischii, and one through the ilium. A pelvic side segment is created and rotation of the acetabular segment rotates the side segment. A plate is used to secure the pelvic side segment at one end, at the ilium. A wire connector is used at the ischii to hold the other end of the segment in place at an awkward angle.
U.S. Pat. No. 4,762,122 to Slocum discloses a six hole dual planar plate having an interconnecting orthogonal web which places the plates at a constant planar angle to each other. This six hole plate, when used in procedures according to Slocum involving the rotation of an acetabular segment, and also used in a more refined procedure which included a transverse osteotomy of both ilium and a secondary osteotomy through the pelvic symphysis, still resulted in loosened or broken screws securing the plate, and loss of bone purchase resulting in the necessity of replacing the plates.
As between the two techniques, the more refined technique of a transverse osteotomy of both ilium and a secondary osteotomy through the pelvic symphysis provides superior results, including a self ambulatory result within about 24 hours of surgery compared to about three days to a self ambulatory state with the ilial section rotation technique. The secondary osteotomy removes bone tissue to accommodate the resulting pelvic narrowing which occurs during rotation of the pelvic segments toward each other.
For a more accurate comparison, pelvic osteotomies were performed in 100 cases involving the more refined technique. It was found that the six hole plate of Slocum was problematic since the angles of the plates were fixed. Since the angles of the six hole plate are determined by the web shape, the angle of the plates could not be changed without either distorting the web shape or distorting the plates by producing a severe twist in their planes.
Further, complications for the six hole plate included broken screws, loosened screws and bilateral loss of bone purchase requiring replacement of screws. The problems encountered were related to the requirement in each case for an angular plate displacement differing from the displacement required for optimum pelvic placement. Also, the physical configuration and placement of the screws were not sufficient for bone retention. In cases where failure occurs, the results to the canine patient are severe. The requirement to surgically re-enter and perform further work is especially difficult on the animal, and requires a period of re-recovery.
Therefore, any technique or apparatus which reduces or eliminates the necessity to surgically re-enter the patient introduces a significant improvement over the currently available techniques and apparatus for performing these surgical techniques.